This randomized intervention trial will test the hypothesis that a daily diet of 5 servings of green and yellow vegetables and 4 servings of fruits (particularly citrus fruits) will reduce the incidence of second primary malignancies among patients with stages I-II head and neck cancer or with stage 1 squamous cell carcinoma of the lung. Since most of these second primary. cancers occur in the respiratory and upper alimentary tracts, the study would provide strong confirmatory evidence for the preventive effect of fruits and vegetables against these cancers that has been suggested in observational studies. The study will also validate a chromosome fragility assay as an intermediate marker. The study will enter approximately 208 Oahu residents diagnosed between January 1993 and June 1997 with squamous cell carcinoma of the head and neck (stage I or II) or of the lung (stage I). Following a run-in period, the subjects will be randomly assigned to an intervention group or a control group. The intervention group will receive an individualized dietary counseling program designed to increase vegetable and fruit consumption to a total of nine servings per day. Vegetable and fruit intakes will be monitored by unannounced food recalls and an abbreviated diet history. Serum levels of carotenoids and ascorbic acid will assess dietary adherence in both groups. All subjects will be followed until the end of 1998 (mean follow-up 3.7 years). During this period, 20% of the subjects are expected to develop a second primary cancer. Change in mutagen sensitivity will be evaluated as an intermediate endpoint. Occurrence of second primary malignancies will be assessed as the primary study endpoint. The successful completion of this study would have important implications for the dietary prevention of respiratory and upper alimentary cancers, and of other cancers as well.